Process for synthesizing compositions containing smectite-type clays and gellants produced thereby

ABSTRACT

This invention provides a process for synthesizing compositions containing trioctahedral smectite-type clays which contain fluorine within their layer lattices. In particular, the invention provides a process for synthesizing compositions having mole ratios of Li, Na, Mg and Si, expressed as oxides, and F of: 
     
         aLi.sub.2 O : bNa.sub.2 O : cMgO : dF : 8SiO.sub.2         (I) 
    
     where 0≦a&lt;1.2, 0≦b&lt;0.6, 4.75≦c&lt;7, 0&lt;d&lt;4, o≦a+b&lt;1.4, and 5.5&lt;a+b+c&lt;8, and where c≧6 when a+ b= 0. The process comprises: (a) forming an aqueous suspension containing from 12% to 35% solids by weight, the solids having the chemical composition represented by formula I, by (i) combining and mixing hydrofluoric acid, magnesia, water, and a base selected from the group consisting of lithium hydroxide, sodium hydroxide, and mixtures thereof, until the base is dissolved; and (ii) adding a silica sol; (b) agitating and heating the suspension until a viscous slurry is obtained; (c) allowing the slurry to gel; (d) hydrothermally reacting the gel under autogenous pressure at a temperature in the range from about 85° C to about 250° C for a period of time sufficient to form a well crystallized trioctahedral smectite-type clay; and (e) drying the product to form the composition. 
     Gellants having a cation exchange capacity within the range from about 70 to 100 milliequivalents per 100 grams, a Bingham Yield Value of at least 50 dynes/cm 2  as a 2% dispersion in water, and the ability to disperse in deionized water at a concentration of 2% by weight to produce a thixotropic gel having a Bingham Yield Value greater than about 20 dynes/cm 2 , the gel having a Bingham Yield Value above 50 dynes/cm 2  upon aging are provided by the process when: 0.25≦a&lt;1.1, 0&lt;b&lt;0.60, 5.85≦c&lt;7.0, 0.5&lt;d≦3.5, 0.5≦a+b&lt;1.3, and 6.5&lt;a+b+c&lt;8.0.

This patent application is a continuation-in-part of our copending patent application Ser. No. 680,593 filed Apr. 26, 1976 now U.S. Pat. No. 4,040,974.

BACKGROUND OF THE INVENTION

The invention relates to synthetic swelling smectite-type clays, particularly to a new process for the manufacture of novel gellants containing smectite-type clays.

PRIOR ART

Academic interest in the synthesis of clay minerals has existed for over forty years. The following listed references particularly pertain to the synthesis of smectite-type clay minerals and to the properties of the synthetic smectite-type clays obtained:

L. l. ames et al, "Factors Effecting Maximum Hydrothermal Stability in Montmorillonites." Am. Mineroalogist 43, 641,648 (1958).

T. baird et al, "Electron Microscope Studies of Synthetic Hectorite." Clay Minerals 9, 250-252 (1971).

T. baird, et al, "An Electron Microscope Study of Magnesium Smectite Synthesis." Clay Minerals 10, 17-26 (1973).

W. eitel, "Silicate Science. Vol. IV. Hydrothermal Silicate Systems" 1966 pp. 288+. "The Systems Water-Silicate-Alumina-Magnesia-Lithium or Sodium Oxide."

G. t. faust et al, "A Restudy of Stevensite and Allied Minerals." Am. Mineralogist 44, 342-370 (1949).

F. h. gillery, "Adsorption -- Desorption Characteristics of Synthetic Montmorillonids in Humid Atmospheres." Am. Mineralogist 44, 806-818 (1959).

R. e. grim, "Clay Mineralogy." 2nd Edition 1968 pp 479-490. Chapter 13. "Synthesis of the Clay Minerals."

M. e. harward et al, "Swelling Properties of Synthetic Smectites in Relation to Lattice Substitutions." Clays and Clay Minerals 13, 209-222 (1964).

S. henin et al, "A Study of the Synthesis of Clay Minerals." Clay Minerals Bulletin 2, 110-115 (1954).

S. henin, "Synthesis of Clay Minerals at Low Temperatures." Clay and Clay Minerals 4, 54-60 (1056).

J. t. liyama et al, "Unusually Stable Saponite in the System Na₂ O-MgO-Al₂ O₃ -SiO₂." Clay Minerals Bulletin 5, 1961-171 (1963).

R. c. johnson et al, "Water-Swelling Synthetic Fluormicas and Fluormontmorillonoids." Bureau of Mines R. I. No. 6235 (1963).

M. koizumi et al, "Synthetic Montmorillonoids with Variable Exchange Capacity." Am. Mineralogist 44, 788-805 (1959).

W. noll, "The Electron Microscope in the Study of Hydrothermal Silicate Reactions." Kolloid Z. 107, 181-90 (1944).

D. m. roy et al, "Synthesis and Stability of Minerals in the System MgO-Al₂ O₃ -SiO₂ -H₂ O." Am. Mineralogist 40, 147-178 (1955).

C. b. sclar et al, "High Pressure Synthesis and Stability of a New Hydronium-Bearing Layer Silicate in the System MgO-SiO₂ -H₂ O." Am. Geophysical Union. Transactions 46, 184 (1965).

H. strese et al, "Synthesis of Magnesium Silicate Gels with Two Dimensional Regular Structure." Z. Anorg. Allg. Chem. 247, 65-95 (1941).

V. stubican et al, "Isomorphous Substitution and Infrared Spectra of the Layer Lattice Silicates." Am. Mineralogist 46, 32-51 (1961).

D. c. warren, et al, "A Morphological Study of Selected Synthetic Clays by Electron Microscopy." Clays and Clay Minerals 16, 271-274 (1968).

C. e. weaver et al, "The Chemistry of Clay Minerals." 1973, pp. 169-172. Chapter 16. "Low Temperature Synthesis."

J. c. yang, "The System magnesia-Silica-Water Below 300° C. L, Low-Temperature Phases from 100° to 300° and Their Properties." J. Am. Ceramic Soc. 43, 542-549 (1960).

Interest in the commercial production of synthetic 2:1 layer-lattice clay minerals commenced in the 1950's with a Fellowship at Carnegie-Mellon University headed by Dr. W. T. Granquist. This research was successful in establishing commercial processes for this hydrothermal synthesis of hectorite-like clays, saponite-like clays, mixed layer-type clays, and other minerals. Subsequently various other companies became active in the field of mineral synthesis, particularly the synthesis of smectite-type clays, especially hectorite-like clays. The following references particularly pertain to such syntheses and to the properties and uses of the synthetic smectite-type clays obtained:

U.s. pat. Nos.

3,252,757 -- Granquist -- Synthetic Silicate Minerals

3,586,478 -- Neumann -- Syn. Hectorite-Type Clay Minerals

3,654,176 -- Neumann and Sansom-Composition and Process for Making Stable Aqueous Sol of Synthetic Silicate

3,666,407 -- Orlemann -- Process for Producing Synthetic Hectorite-Type Clays

3,671,190 -- Neumann -- Synthetic Clay-Like Minerals of the Smectite Type and Method of Preparation

3,839,389 -- Organophilic Swelling Clays -- Neumann

3,844,978 -- Hickson -- Layered Clay Minerals and Processes for Using

3,852,076 -- Grasko -- Aqueous Method of Microencapsulation of Capsules

3,852,405 -- Granquist -- Laminar Heavy Metal Aluminosilicates

3,855,147 -- Granquist -- Synthetic Smectite Compositions, Their Preparation, and Their Use as Thickeners in Aqueous Systems

Great Britain Patents

1,255,595 -- Neumann -- Compositions Containing Clay-like Minerals

1,228,155 -- Neumann -- Clay Compositions

1,276,016 -- Neumann and Sansom -- Synthetic Silicate Compositions

1,294,253 -- Pfizer, Inc. -- Use of Synthetic Clay Containing No Lithium as Soil Anti-Redeposition Agent, in Detergents

1,298,201 -- Sellars and Laybourn -- Paints

Articles

W. t. granquist et al, "A Study of the Synthesis of Hecterite." Clays and Clay Minerals 8, 150-169 (1959).

B. s. neumann, "Behavior of a Synthetic Clay in Pigment Dispersions." Rheologica Acta 4, 250-255 (1965).

B. s. neumann et al, "The Formation of Stable Sols from Laponite, A Synthetic Hectorite-Like Clay." Clay Minerals 8, 389-404 (1970).

B. s. neumann et al, "The Rheological Properties of Dispersions of Laponite, A Synthetic Hectorite-Like Clay, in Electrolyte Solutions." Clay Minerals 9, 231-243 (1971).

R. perkins et al, "Colloid and Surface Properties of Clay Suspensions. 1. Laponite CP." J. Coll. Interface Sc. 48, 417-426 (1974).

J. taylor et al, "The Nature of Synthetic Swelling Clays and Their Use in Emulsion Paint." J. Oil Col. Chem. Assoc. 51, 232-253 (1968).

The structure of 2:1 layer-Lattice clay minerals is well known. Such minerals contain a central layer of cations octahedrally coordinated to oxygen and hydroxyl anions which are linked through shared oxygen anions to two layers of cations tetrahedrally coordinated to oxygen and hydroxyl anions, one on each side of the central octahedral layer. Fluorine may substitute for the hydroxyl groups. For each unit cell of such clays there are 6 octahedral cation sites and 8 tetrahedral cation sites. The sum of the cationic charges for electroneutrality of the layer-lattice is 12 for the octahedral cation sites and =for the tetrahedral cation sites. Thus the 6 octahedral cation sites can be filled with 6 divalent (+2) cations which satisfies the required layer charge. Clays which contain approximately 6 octahedrally coordinated cations are called trioctahedral. The theoretical formula without considering lattice substitutions for trioctahedral 2:1 layer-lattice clay minerals is

    [(R.sup.+2.sub. 6) VI  (D.sup.+4).sub.8.sup.IV O.sub.20 (OH).sub.4 ]n H.sub.2 O (interlayer water).

The number of cations in the octahedral layer of naturally occurring trioctahedral 2:1 layer-lattice clay minerals is within the range from 5.76 to 6.00. However, the 6 octahedral cation sites can also be filled with 4 trivalent (+3) cations which satisfies the required layer charge. Such clays which contain approximately 4 octahedrally coordinated cations are called dioctahedral. The theoretical formula without considering lattice substitutions for dioctahedral 2:1 layer-lattice clay minerals is

    [ (R.sup.+3).sub. 4.sup.VI (D.sup.+4).sub.8.sup.IV O.sub.20 (OH).sub.4 ] .nH.sub.2 O (interlayer water).

The number of cations in the octahedral layer of naturally occurring dioctahedral 2:1 layer-lattice clay minerals is within the range from 4.00 to 4.44.

The octahedrally coordinated cation sites can accommodate cations which have an ionic radius not greater than 0.75 A and the tetrahedrally coordinated cations sites can accommodate cations which have an ionic radius not greater than 0.64 A. Thus various cations can isomorphously substitute for the divalent cations in the central octahedral layer of trioctahedral clays, for the trivalent cations in the central octahedral layer of dioctahedral minerals, and for the tetravalent cations in the outer tetrahedral of both types of minerals. Such substitutions give rise to a charge imbalance within the octahedral and tetrahedral layers in which the substitution occurs. The charge imbalance usually results from the substitution of a cation with a smaller cation charge thus creating a negatively charged layer-lattice. This negative charge is neutralized by cations on the surface of the layer lattices.

Naturally occurring hectorite is a trioctahedral 2:1 layer-lattice magnesium silicate smectite clay mineral in which approximately 0.66 Li⁺ ions per unit cell substittue for 0.66 Mg²⁺ and approximately 1 F⁻ ion per unit cell substitute for OH⁻. Thus the idealized structural formula for natural hectorite is:

    [(Mg.sub.5.34.sup.+2 Li.sub.0.66.sup.+).sup.VI (Si).sub.8.sup.IV O.sub.20 (OH).sub.3 F](0.66/z)M.sup.z+.nH.sub.2 O (interlayer)

where the Mg+Li are present in the central octahedral layer and M is the charge balancing cation external to the layer-lattices of valance z. Hectorite-type minerals can be synthesized in which the number of Li⁺ per unit cell can be varied up to about 1.0 and in which F⁻ can be substituted for OH⁻. Thus hectorite-type minerals have the following idealized structural formula:

    [(Mg.sub.6-r.sup.2+ Li.sub.r.sup.+).sup.VI Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ](r/z)M.sup.z+.nH.sub.2 O (interlayer)            (1)

where 0<r≦1 and 0≦d≦4. The formula is "idealized" since minor amounts of trivalent cations can substitute in both the octahedral layer and the tetrahedral layers and other divalent cations can substitute for Mg. Natural hectorite is also impure and contains such contaminants as calcite, dolomite and other minerals.

Naturally occurring stevensite is a trioctahedral 2:1 layer-lattice magnesium silicate smectite clay mineral in which the octahedral layer contains only about 5.84 Mg²⁺ /unit cell. The idealized structural formula for stevensite is

    [(Mg.sub.5.84.sup.+2).sup.VI Si.sub.8 O.sub.20 (OH).sub.4 ](0.32/z)M.sup. z+.nH.sub.2 O (interlayer).

Stevensite-type minerals can be synthesized in which the number of vacant cation sites in the octahedral layer varies up to about 0.5 and in which F⁻ can be substituted for the hydroxyl groups. Thus stevensite-type minerals have the following idealized structural formula:

    [(Mg.sub.6-s.sup.2+).sup.VI Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ](2s/z)M.sup.z+.nH.sub.2 O (interlayer)                   (2)

where 0>s≦0.5 and 0≦d≦4. As with hectorite-type minerals, the formula is "idealized" since minor amounts of trivalent cations can substitute in both the octahedral layer and is the tetrahedral layers and divalent cations can substitute for Mg.

As disclosed by Granquist and Pollack in the Clays and Clay Minerals article, hectorite-like clays can be prepared at reflux tempratures starting with an aqueous slurry of freshly precipitated Mg(OH)₂, silica gel, sodium hydroxide and/or lithium hydroxide or lithium fluoride. The synthetic clays so prepared are stated to have rheological characteristics in aqueous systems similar to those of natural hectorite. Neumann in example 7 of U.S. Pat. No. 3,586,478 repeated the most successful synthesis given in the Granquist and Pollack article, Series IB-72, and obtained a hectorite-like clay which possessed poor rheological characteristic in aqueous systems.

U.S. Pat. No. 3,586,478 discloses a hydrothermal process for preparing hectorite-like clays in which, in formula (1) 0.38≦r≦0.92 when M=Na⁺, corresponding to a cation exchange capacity for the clay of from 50 milliequivalents per 100g. to 120 milliequivalents per 100g., and 1≦d≦4. These hectorite-type clays, produced commercially under the tradename Laponite B, when dispersed in tap water at 2% have excellent rheological characteristics since they produce dispersions having a Bingham Yield Value of at least 40 dynes/cm², normally up to 250 dynes/cm². The claimed process comprises: (a) forming an aqueous slurry with heating and agitation by co-precipitation of a water-soluble magnesium salt, sodium silicate, and either sodium carbonate or sodium hydroxide, in an aqueous medium containing either lithium fluoride or a lithium compound and a compound containing fluorine chosen from hydrofluoric acid, fluosilicic acid, sodium silicofluoride, or sodium fluoride in certain atomic ratios of Si, Mg, Li and F; (b) hydrothermally treating the slurry, without washing it free from soluble salts, for about 10 to 20 hours to crystallize the synthetic hectorite-like clay; (c) washing and dewatering the clay; and (d) drying the clay at a temperature up to 450° C. Co-precipitation is critical in the claimed process as is the presence of the alkali and fluoride during the co-precipitation. It is also necessary to avoid washing the slurry free from soluble salts.

It is readily apparent to one skilled in the art that the process claimed in U.S. Pat. No. 3,586,478 is very expensive and wasteful since it requires lithium, fluorine and sodium to be present during the synthesis of the hectorite-like clay in quantities which are far in excess of the stoichiometric quantities incorporated into the hectorite-like clay, and thereafter these soluble salts must be washed out of the product. A slightly excessive amount of magnesium is also present in the feed slurry during the synthesis. The following table presents the number of moles of Mg, Li, F, and Na present in the feed compositions and the hectorite-like clay products obtained based on the presence of eight moles of silicon, in Examples 1, 2, 3, 4 and 5 of U.S. Pat. No. 3,586,478.

    __________________________________________________________________________     Moles in Feed Slurry Moles in Product                                          Calculated           Chemical Analysis                                         Example                                                                             Mg  Li  F   Na  Mg   Li  F   Na                                           __________________________________________________________________________     1    6.0 3.0 3.0 12.0                                                                               (5.8)*                                                                              0.53                                                                               2.0 0.53                                         2    6.0 2.4 2.4 12.0                                                                               5.52 0.48                                                                               1.5 0.48                                         3    6.0 4.0 9.0 17.3                                                                               5.43 0.57                                                                               2.77                                                                               0.57                                         4    6.0 0.8 3.6 14.8                                                                               5.65 0.35                                                                               1.7 0.35                                         5    6.0 6.0 6.0 12.0                                                                               5.41 0.59                                                                               2.53                                                                               0.59                                         __________________________________________________________________________      *This value is suspect since Mg + Li>6.0                                 

This process is also expensive due to the low concentration (1%-8%) of hectorite-like clay synthesized after hydrothermal treatment of the feed slurry, and because of the use of expensive water soluble magnesium salts. Furthermore, as all of the examples in the patent indicate, the feed slurry must be efficiently stirred during the hydrothermal treatment of the feed slurry in order to prevent settling and the formation of a non-homogeneous slurry.

Neumann U.S. Pat. No. 3,671,190 discloses synthetic trioctahedral smectite-type clay-like minerals and a process for their preparation wherein the smectite-type mineral has the general structural formula:

    [Mg.sub.a Li.sub.b H.sub.4+c Si.sub.8 O.sub.24].sup.(12-2a-b-c)- . (12-2a- b-c)M.sup.+

where:

(i) M is Na⁺, Li³⁰ or an equivalent of an organic cation;

(ii) the values of a a, b and c are such that either:

    a<6, b>0, c>0; b+c<2; .sub.-.sup.+ (a+b+c-6)< 2

or

    a<6, b=0, .sub.-.sup.+ c<2; .sub.-.sup.30 (a+c-6)<2;

(iii) 0.37<(12-2a-b-c)<0.93 which corresponds to a cation exchange capacity of about 50 to 120 meq./100g.; and wherein

iv. when M is Na⁺ or Li⁺, a Bingham yield value of at least 50 dynes/sq. cm. as a 2% dispersion in tap water.

The disloced process is very similar to that disclosed in U.S. Pat. No. 3,586,473, except that the hydrothermal treatment of the reaction slurry is conducted at a temperature of at least 170° C when lithium is present and at least 207° C when lithium is absent.

This process is also expensive to conduct due to: the low concentraation of smectite-type clay synthesized (less than about 5%); the use of expensive water soluble magnesium salts; the necessity for using high temperature, high pressure stirred autoclaves; and the necessity for using lithium, sodium, and silicon compounds during the synthesis of the smectite-type clay which are in excess of the stoichiometric quantities of these metals incorporated into the clay, and which are subsequently filtered and washed out of the clay.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a process for the synthesis of compositions containing a fluorine-containing trioctahedral smectite-type clay which utilizes stoichiometric quantities of the metals and fluorine incorporated into he composition, which utilizes magnesia as the source of magnesium, which utilizes a gel-state synthesis and thus requires no mixing during prolonged hydrothermal treatment of the feed, which requires no filtration and washing of the composition, and in which the concentration of solids in the feed, and hence the concentration of the composition synthesized, can be varied up to about 35% by weight.

The process comprises:

a. forming an aqueous suspension containing from 12% to 35% solids by weight, the solids having the following empirical formula on a moisture free, ignited basis:

    aLi.sub.2 O : bNa.sub.2 O : cMgO : dF : 8SiO.sub.2         (I)

where 0≦a<1.2, 0≦b<0.6 4.75≦c<7 0<d<4, 0≦a+b<1.4, and 5.5<a+b+c<8, and where c≧6 when a+b=0, by (i) combining and mixing hydrofluoric acid, magnesia, water, and a base selected from the group consisting of lithium hydroxide sodium hydroxide, and mixtures thereof, until the base is dissolved; and (ii) adding a silica sol;

b. agitating and heating the suspension until a viscous slurry is obtained;

c. allowing the slurry to gel; and

d. hydrothermally reacting the gel under autogenous pressure at a temperature within the range from about 85° C to about 250° C for a period of time sufficient to form said well crystallized fluorine-containing trioctahedral smectite-type clay; and

e. drying the product obtained from said hydrothermal treatment.

It is another object of this invention to provide gellants which have a cation exchange capacity of about 0.7 to 1.0 milliequivalents per gram, a Bingham Yield Value of at least 50 dynes/cm² as a 2% dispersion in water, and the ability to disperse in deionized water at a concentration of 2% to produce a thixotropic gel having a Bingham Yield Value greater than 20 dynes/cm², the gel having a Bingham Yield Value above 50 dynes/cm² upon aging, the gellant comprising a synthesized complex of a fluorine-containing trioctahedral smectite-type clay and an occluded amorphous phase selected from the group consisting of lithium hydroxide, sodium hydroxide, magnesium hydroxide, lithium oxide, sodium oxide, magnesium oxide, and mixtures thereof, the gellant containing mole ratios of Li, Na, Mg and Si, expressed as oxides, and F of aLi₂ O : bNa₂ O : cMgO : dF : 8SiO₂ where 0.25 ≦a<1.1, 0<b<0.60, 5.85<c<7.0, 0.5<d≦3.5, 0.5<a+b< 1.3, and 6.5<a+b+c<8.0.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS

As indicated, the first step (a) in the process of this invention comprises forming an aqueous suspension containing from 12% to 35% solids by weight, preferably at least 15%, the solids having the chemical composition represented by formula I. The suspension is formed by (i) mixing together hydrofluoric acid (HF), magnesia (MgO), water, and a base selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH) or mixtures thereof, until the base is dissolved; and (ii) adding a silica sol.

In step (i) the order of addition of the MgO, HF, base and water is not critical in synthesizing the fluorine-containing trioctahedral smectite-type clay compositions. However, it is preferred that the magnesia is reacted with the HF before addition of the base. Preferably the magnesia is mixed into the water before slowly adding the HF. Because the reaction of the HF and MgO is exothermic, the HF must be added slowly while allowing the mixing to evenly distribute the heat involved in order to eliminate "bumping" which occurs due to localized reactions. The HF is added as an aqueous solution conveniently containing from 20% - 70% HF, preferably 25% to 35%. The concentration of MgO and HF in this step must be such that the concentration of solids in the gel, produced later, is within the range from 12% to 35%. The maximum concentration of MgO is limited to less than about 30%. It is sufficient to mix the HF, MgO and water together until the reaction is complete, which is indicated when the temperature of the reaction mixture ceases to rise. Generally five minutes is sufficient although a longer mixing time is not harmful.

Thereafter NaOH and/or LiOH, as required by formula I, is added to the MgO + HF suspension and mixing until the base is dissolved. Preferaly the base is added as a solid in order that the heat of reaction of the base with the suspension is utilized to increase the temperature of the suspension. However, the base can be added as an aqueous solution provided that the concentration of the base is such that the final gel will contain from 12% to 35% solids.

In step (ii) a silica sol is added while mixing and the mixing is thereafter continued in step (b), with heating of the suspension until a viscous slurry is obtained. The viscosity of the mixture upon addition of the silica sol increases to a maximum and then decreases as the remainder of the silica sol is added. Depending on the composition of the mixture, the final mixture may be extremely fluid to viscous. However, on continued mixing with heating in step (b) the viscosity of the mixture decreases producing a fluid suspension which must be stirred to prevent settling of solids until the viscosity increases such that the solids no longer settle and an irreversibly viscous slurry is obtained. Preferably only gentle agitation is needed to keep the solids suspended. A low rpm mixer is sufficient. It is believed that, during this heating and mixing step, synthetic smectite-type clay microcrystals are formed which increase the viscosity of the suspension - first creating a viscous homogenous slurry from which no settling occurs, and finally a gel in step (c) as more hectorite-like clay is synthesized. The apparent viscosity of the slurry, as measured with a Fann rotational viscometer (API Standard Procedure RP 13B, November, 1972), should be at least 10 centipoise (cp.), preferably at least 15 cp., in order to keep the solids from settling.

In step (c) this viscous slurry is allowed to gel, with or without stirring. Conveniently, during step (c), the slurry is removed from the vessel containing the agitating means and is transferred to the vessel where the gel is to be statically hydrothermally treated in step (d).

The hydrothermal treatment of the gel in step (d) may be carried out at any conveninent temperature above about 85° C, preferably from 85° C to about 250° C, under autogenous pressure. Since the pressure rapidly increases above about 165° C, thus requiring special autoclaves as the reaction vessel, it is preferred to operate at temperatures in the range from about 85° C to 165° C, preferably from 95° C to 165° C. The gel is hydrothermally treated for a period of time sufficient to synthesize a well crystallized trioctahedral smectite-type clay. Generally from 4 hours to 120 hours is sufficient depending on the temperature. As the temperature increases the required hydrothermal treatment time decreases.

Finally, in step (e) the product resulting from the hydrothermal treatment is dried to produce the desired composition. Before drying the product is a waxy solid containing from about 65 % to about 85% water. The drying temperature should be less than about 400° C, preferably less than about 250° C. Preferably the composition contains from 0.5% to 10% water determined by measuring the weight lost on drying the composition overnight at 105° C.

Generally it has been observed that the rate of viscosity increase of the viscous slurry can be decreased by increasing the degree of shear applied to the slurry. Thus if the viscous slurry is transferred to another vessel during step (c), the rate of viscosity increase of the slurry can be decreased by increasing the mixing rate of the slurry. This wall decrease the possiblity of premature gelation of the slurry before the transfer is complete. It has also been occasionally observed that when the degree of shear applied to the suspension in step (b) is increased the reaction time to form a viscous slurry is increased. The reason for this is not known. Thus it is preferred that a minimum degree of shear be applied to the suspension in step (b), the agitation being sufficient to keep the solids suspended. Intermittant mixing is sufficient.

Optionally the mixture of water, magnesia, hydrofluoric acid and base can be subjected to a high degree of shear, such as is imparted by a colloid mill, to reduce the particle size of the magnesia. The suspension obtained after adding the silica sol can also be subjected to a high degree of shear. It has been determined that such shearing produces compositions that form clearer dispersions in water.

Silica sols are commercially available from E.I. Dupont de Nemous & Co., Inc. Nalco Chemical Co., and other companies. The surface area of the silica in the sols must be greater than 100 square meters per gram (sq.m./g.), preferably greater than 200 sq.m./g. The reactivity of the silica increases as the surface area increases. Hence, as the surface area of the silica increases: the time required for the suspension to form a viscous slurry decreases; the time required for the slurry to gel decreases and the hydrodthermal treatment time decreases. Representative commercially available silica sols are listed in Table 1.

                                      Table 1                                      __________________________________________________________________________     Colloidal Silica Sols                                                          Company   DuPont (LUDOX Products)                                              Type      HS-40 HS    AS    LS    SM-30 TM                                     Stabilizing                                                                    Counter Ion                                                                              Na.sup.+                                                                             Na.sup.+                                                                             NH.sub.4.sup.+                                                                       Na.sup.+                                                                             Na.sup.+                                                                             Na.sup.+                               Particle, Size,                                                                mμ     13-14 13-14 13-14 15-16 7-8   22-25                                  Specific Surface                                                               Area, sq.m./g.                                                                           210-230                                                                              210-230                                                                              210-230                                                                              195-215                                                                              375-420                                                                              125-14                                 Silica (SiO.sub.2)                                                             wt. %     40.0  30.0  30.0  30.0  30.0  >40.0                                  pH at 25° C                                                                       9.7   9.8   9.6   8.4   9.9   8.9                                    SiO.sub.2 /Na.sub.2 O                                                          (by wt.)  93    93    120*  300   50    230                                    Company   Nalco Chemical Co. (NALCOAG Products)                                Type      1130  1030  1140  1050  1034A                                        Stabilizing                                                                    Counter Ion                                                                              Na.sup.+                                                                             Na.sup.+                                                                             Na.sup.+                                                                             Na.sup.+                                                                             H.sup.+                                      Particle Size,                                                                 mμ     8     13    15    20    20                                           Specific Surface                                                               Area, sq.m./g.                                                                           375   230   200   150   150                                          Silica (SiO.sub.2)                                                             wt. %     30    30    40    50    34                                           pH at 25° C                                                                       10.0  10.2  9.7   9.0   3.2                                          SiO.sub.2 /Na.sub. 2 0                                                         (by wt.)  46    75    100   143   >680                                         __________________________________________________________________________      *SiO.sub.2 /NH.sub.3 (by wt.)                                            

The concentration of silica in the sol must be sufficiently large that the concentration of solids in the suspension after adding the silica sol is from 12% to 35%, preferably from 15% to 35% by weight. Thus depending on the composition of the gellant and the concentration of solids before adding the silica sol, the silica sol should contain at least 10% silica.

Any uniformly calcined magnesia having a BET nitrogen surface area in excess of about 10 m.² /g. and a magnesia content of greater than about 95% on an ignited basis may be employed. Typically bulk magnesia contains a mixture of periclase (MgO) and brucite (Mg(OH)₂) depending on the degree of rehydration following calcination. The ratio of these components appears to have little effect on the synthesis process provided a high surface area is maintained. The preferred mesh size is -200M so that rapid settling in the initial feed mixture is minimized. Several commercially available magnesias which meet these criteria are Fisher M- 49 grade, Michigan 15 and 1782 from Michigan Chemicals, Magox HR98 and HR98 Fine from Basic Chemicals and Dow 5800 magnesium oxide from Dow Chemical Co.

Six features of the process of this invention merit special attention. All are critical and contribute to the success of the process as a commercially operable process and as a means of producing a gellant containing a fluorine-containing trioctahedral smectite-type mineral which possesses commercially desirable properties.

The first feature is that only stoichiometric quantities of the metals and fluorine which are desired in the composition are present during the synthesis of the compositions.

Secondly, the source of magnesium is magnesium oxide which is commercially available and less expensive than other purified magnesium compounds.

Thirdly, a silica sol is used as the source of silica. The sol must be added to the reaction mixture only after all of the other desired components of the mixture have been combined.

Fourth, the process requires a high solids content in the feed suspension and thereafter. This results in higher production rates and lower production costs.

Fifth, the reaction mixture is gelled during the hydrothermal treatment. This eliminates the necessity of stirring the mixture with all the problems attendent thereto. The hydrothermal treatment may simply be carried out by heating the gelled feed in a suitable closed container in an oven set at the desired temperature.

Sixth, the process requires no filtration and washing of the composition and, indeed, filtration is not practicable since the un-dried composition is a waxy solid and washing is detrimental in that any excess base that is required to be present in the composition of this invention would be removed.

The compositions produced by the process of this invention contain at least one fluorine-containing trioctahedral smectitetype clay. The compositions have mole ratios of Li, Na, Mg, and Si, expressed as oxides, and F of:

    aLi.sub.2 O : bNa.sub.2 O : cMgO : df : 8SiO.sub.2         (I)

where 0≦a<1.2, 0≦b<0.6, 4.75≦C<7 0<d<4, 0≦a+b<1.4, and 5.5<a+b+c<8, and where c≧6 when a+b=0. In addition to the smectite-type clay the compositions may contain occluded amorphous phases selected from the group consisting of the oxides and hydroxides of Li, Na, and Mg, and mixtures thereof. Thus when a=0 and b+c<6.0, there are obtained smectite-type clays having the structural formula

    [Mg.sub.c H.sub.h Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup.(12-2c-h)- (12-2c-h)Na.sup.+                                         (i)

When a=0 and b+c=6.0, there may be obtained (1) stevensite-like clays having the structural formula

    [Mg.sub.c Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup. (12- 2c)- (12-2c)Na.sup.+ (ii);

and (2) smectite-type clays having the same structure as the clays indicated with formula (i) complexed with an occluded amorphous phase selected from the group consisting of magnesium oxide, magnesium hydroxide, sodium oxide, sodium hydroxide, and mixtures thereof. Thus the composition can be considered as having the empirical formula

    {[Mg.sub.m H.sub.h Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup.x- xNa.sup.+ } + {nMg(O,(OH).sub. 2) + pNa(OH,1/20)}         (iii

where x=12-2m-h c=m+n, b=(+p)÷2, n≧0 and p≧0, and where the composition in the first braces represents the smectite-type clay, or mixture of clays and the composition in the second braces represents the occluded phases.

When a=0 and b+c>6.0, there may be obtained 1. talc-like clay when b=0 having the structural formula [Mg₆ Si₈ O₂₀ (OH)_(4-d) F_(d) ] complexed with an occluded amorphous phase selected from the group consisting of magnesium oxide, magnesium hydroxide, and mixtures thereof, such compositions having the empirical formula

    {[Mg.sub.6 Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ]} + {nMg(O, (OH).sub.2)}

where c=6+n and n>0, and where the composition in the first braces represents the talc-like clay and the composition in the second braces represents the occluded phases;

2. stevensite-like clays having the same structure as the clays indicated with formula (ii) complexed with an occluded amorphous phase selected from the group consisting of magnesium oxide, magnesium hydroxide, sodium oxide, sodium hydroxide, and mixtures thereof, such compositions having the empirical formula

    {[Mg.sub.m Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup. x- xNa.sup.+ } + {nMg(O, (OH).sub.2) + pNa(OH, 1/20)}

where x=12-2m, c= m+n, b=(x+p)÷2; n≧0, p≧0, and where the composition in the first braces represents the stevensite-like clay and the composition in the second braces represents the occluded phases; and

3. compositions having the empirical formula (iii).

Where a>0 and a+b+c<6.0, there are obtained smectite-type clays having the empirical formula

    [Mg.sub.c Li.sub.q H.sub.h Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup.x- x(yLi.sup.+ +zNa.sup.+)                                   (iv)

where h>0, x=12-2c-q-h, y+z=1, a=(1+xy)÷2, and b=xz÷2. Where a>0 and a+b+c=6.0, there may be obtained (1) hectoritelike clays having the structural formula

    [Mg.sub.6-x Li.sub.x Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup. x(yLi.sup.+ +zNa.sup.+)                                   (v)

where y+z=1, c=6-x, a=(x+xy)÷2, and b=xz÷2; and

2. smectite-type clays having the same structure as the clays indicated with formula (iv) complexed with an occluded phase selected from the group consisting of magnesium oxide, magnesium hydroxide, sodium oxide, sodium hydroxide, lithium oxide, lithium hydroxide, and mixtures thereof, such compositions having the empirical formula

    {[Mg.sub.m Li.sub.q H.sub.h Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup.x- x[yLi.sup.+ +zNa.sup.+ ]}+  {nMg(O, (OH).sub.2)+ pNa(OH,1/20)  + r(OH, 1/20)}                                                    (vi)

where x=12-2 m-q-h, y+z=1, c=m+n, a=(q+y+r)÷2, b=(xz+p)÷2,

≦0, p≦O, r≦0 and where the compositions in the first braces represents the smectite-type clay and the composition in the second braces represents the occluded phases. When a>0 and a+b+c>6.0, there may be obtained (1 ) hectorite-like clays having the same structure as the clays indicated with formula (v) complexed with an occluded phase selected from the group consisting of magnesium oxide, magnesium hydroxide, lithium oxide, lithium hydroxide, sodium oxide, sodium hydroxide, and mixtures thereof, such compositions having the empirical formula

    {[Mg.sub.6-x Li.sub.x Si.sub.8 O.sub.20 (OH).sub.4-d F.sub.d ].sup.x- x[yLi.sup.+ +zNa.sup.+ ]} +

    {nMg(O, (OH).sub.2) + pNa(OH, 1/20) + qLi(OH, 1/20)}

where y+z=1, c=6-x+n, a=(x+xy+q)÷2, b=(xz+p)÷2, n≧0, p≧o, g≧0, and where the composition in the first braces represents the hectorite-like clay and the composition in the second braces represents the occluded phases; and 2. compositions having the empirical formula (vi).

The compositions produced by the process as disclosed may be useful as thickeners/gelling agents fro aqueous systems as disclosed in Neumann U.S. Pat. No. 3,586,478 and Neumann U.S. Pat. No. 3,671,190, each incorporated herein by reference. The compositions may also be useful in preparing: refractory laminates as disclosed in Bever et al. U.S. Pat. No. 3,878,034, incorporated herein by reference; multi-color aqueous paints, etc., as disclosed in Zola U.S. Pat. No. 3,458,328, incorporated herein by reference; detergent compositions as disclosed in Nirschl et al, U.S. Pat. No. 3,862,058, incorporated herein by reference, and pesticidal formulations as disclosed in Hyson et al, U.S. Pat. No. 3,832,468, incorporated herein by reference.

The preferred compositions produced by the process of this invention have a cation exchange capacity (CEC) of about 0.7 to 1.2 milliequivalents per gram (meq./g.) and have mole ratios of Li, Na, Mg, and Si, expressed as oxides, and F of:

    aLi.sub.2 O : bNa.sub.2 O : cMgO : dF : 8SiO.sub.2

where 0.25≦a<1.1, 0≦b<0.60, 5.0≦c<6.75, 0.5<d<4, 0.60≦a+b<1.4, and 6.0<a+b+c≦8. More preferably 1.0≦d≦3.5. Compositions synthesized within these mole ratio ranges are excellent gellants for aqueous systems. All compositions wherein a+b+c>6.0 are synthesized complexes of a trioctahedral smectite-type clay and an amorphous occluded compound selected from the group consisting of lithium hydroxide, sodium hydroxide, magnesium hydroxide, lithium oxide, sodium oxide, magnesium oxide, and mixtures thereof.

Compositions wherein 0.25≦a<1.1, 0≦b<0.60, 5.0≦c<5.85, 1.0≦d≦3.5, 0.60≦a+b<1.25, 6.0<a+b+c<6.65, and 0.70≦CEC≦1.2 have the following characteristics: (a) the ability to disperse within 15 minutes in deionized water at a concentration of 2% to produce a sol having a low viscosity and a Bingham Yield Value less than about 20 dynes/cm², which sol is converted within 48 hours to a thixotropic gel having a Bingham Yield Value greater than about 50 dynes/cm² ; and (b) a Bingham Yield Value of at least 50 dynes/cm² as a 2% dispersion in water containing 4-10 meq./l. of Ca²⁺ and/or Mg²⁺. Compositions wherein 0.50<a<1.05, 0≦b<0.50, 5.0≦c<5.85, 1.5≦d≦3.5, 0.60<a+b<1.25, 6.0<a+b+c<6.65, and 0.80 ≦CEC≦1.13, additionally produce dispersions at 2% in deionized water which have at least 85% light transmission within 48 hours after preparation of the dispersions, as measured with a Hach Meter (water=100% transmission) having a filter with a Corning number of 5330. Compositions wherein 0.50<a<0.80, 0≦b<0.50, 5.1<c<5.7, 1.5<d<3.0, 0.60<a+b<1.0, 6.025<a+b+c<6.4, and 0.80≦CEC≦1.00, produce dispersions under these conditions which have at least 90% light transmission.

Compositions wherein 0.25≦a<1.1, 0<b<0.60, 5.85≦c<7.0, 0.5<d≦3.5, 0.5<a+b<1.3, 6.5<a+b+c<8. and 0.70≦CEC≦1.0, when dispersed in deionized water at a concentration of 2% produce Bingham Yield Values in excess of 20 dynes/cm². The Bingham Yield Values of these dispersions increase with time such that thixotropic gels having a Bingham Yield Value greater than 50 dynes/cm² are obtained within 48 hours.

The smectite-type clay in the compositions when first formed as disclosed have an exchangeable cation which is Li⁺, Na⁺ or a mixture thereof, except when talc-like clay is synthesized. These cations can be exchanged with other cations to form other commercially useful products. Thus these cations can be exchanged with a metallic cation having a Pauling electronegativity greater than 1.0 to form catalytically active materials. Such materials are especially active catalysts for the alkylation of aromatic hydrocarbons with alkyl halides and/or unsaturated hydrocarbons such as alkenes when the cation exchange capacity of the composition is in excess of about 0.75 meg./g. These catalysts are also useful as components of hydrocarbon cracking catalysts, hydrotreating catalysts, and the like.

The exchangeable Li⁺ and Na⁺ can be replaced with an organic cation to form organophilic gellants for organic systems. These organophilic gellants which are useful in making greases and as suspending agents in organic systems such as paints may be prepared by dispersing the gellant in water and reacting the gellant with the organic compound. The gellant is readily flocculated. Filtration and washing of the organophilic gellant results in removal of essentially all of the sodium and all of the lithium except that which is present within the octahedral layer of the smectite-type clay when the amount of organic compound is at least equal to the exchange capacity of the gellant. The excess magnesium oxide or magnesium hydroxide which is present in the gellants remains as an occluded phase in the organophilic gellants. The amount of organic cation should be at least equal to the cation exchange capacity of the gellant, preferably from 100 to 250 milliequivalents of organic compound per 100 grams of gellant.

Examples of organic comounds or salts thereof which will react with the gellants are those compounds which contain at least one cation per molecule selected from the group consisting of ammonium, phosphonium, oxonium, sulphonium, arsonium, stibonium, and mixtures thereof. Preferred are organic ammonium salts, particularly quaternary ammonium salts. Preferably the organic cation contains at least one aliphatic group, more preferably an alkyl group, containing at least 10 carbon atoms, desirably at least 12 carbon atoms. Advantageously the organic cation contains a total of at least 18 carbon atoms. Specific examples of suitable organic cations are dimethyl dioctadecyl ammonium, dimethyl benzyl dodecyl ammonium, dimethyl benzyl hydrogenatedtallow ammonium, methyl benzyl dihydrogenatedtallow ammonium, trimethyl hexadecyl ammonium, trimethyl behenyl ammonium, and mixtures thereof.

In the examples, the following starting materials were used unless otherwise noted: the silica source was Nalcoag 1130, a sodium stabilized silica sol containing 30.0% SiO₂ and 0.65% Na₂ O; the magnesia source was Magox HR98, a high surface area (136 m.² /g.) calcined magnesite containing 98% MgO on a volatile free basis having a particle size such that 99% passes through a 200 mesh screen; the lithium source was technical LiOH.H₂ O containing 56.6% LiOH; the soda source was a Fisher Chemical Co. standardized 10N NaOH solution; the fluoride source was technical hydrofluoric acid containing 70% HF which was diluted with water before use to a final HF concentration of 37.1%.

EXAMPLE 1

Samples were prepared by changing the values of a, b, c, a+b, and a+b+c in formula I within the following ranges: 0≦a≦1.185; 0.165≦b≦0.70; 4.75≦c≦7.1; 0.4≦a+b≦1.35; 6.0≦a+b+c≦7.525. All of these samples contained 2.25F/8SiO₂ (d=2.25) and were prepared at 22.5% solids. The compositon of each sample is given in Table 2A. The samples were prepared using the following procedure. The required amount of magnesia was mixed with water in an amount such that the final feed contained 22.5% solids. All of the HF was slowly added and the mixing was continued for 5 minutes. The lithium hydroxide and sodium hydroxide, as required, were added and the mixing was continued for 5 minutes until all of the base dissolved. Thereafter the silica sol was added and mixed for 10 minutes. The suspensions obtained, which varied from viscous gels to low viscosity liquids, were placed in glass bottles, capped, and placed in an oven at a temperature of 100° C. The suspensions were periodically mixed to keep the solids suspended until irreversibly viscous slurries were obtained from which no solids would settle. The slurries were then allowed to gel and thereafter maintained in the oven at 100° C for 72 hours. The waxy solid gels obtained were dried at 120° C for 16 hours.

The cation exchange capacities (CEC) of the samples were determined as well as their ease of dispersion in deionized water, which was determined as follows: 0.20 grams of < 100 mesh sample was added to 9.80 milliliters of deionized water in a bottle and the mixture shaken by hand frequently for up to 2 hours. The "dispersion time" was determined by measuring the time for the particles to disperse as judged by the absence of any particles adhering to the sides of the bottle above the liquid meniscus. The data obtained are given in Table 2A. All of the samples were well crystallized trioctahedral smectite-type clays, as determined by X-ray diffraction, with a 060 (hkl) diffraction band between 60.85 and 61.25°2θ except samples 58 and 60 which were amorphous. The samples containing a smectite-type clay were evaluated for their viscosity building characteristics by preparing 2% dispersions in deionized water and obtaining rotatonal (Fann-type) viscosimeter rheology data initially and after 24 and 48 hours. The clarity of these dispersions were measured by determining the percent transmittance witjh a Hach meter (water = 100% transmittance) having a filter with a Corning number of 5330. The data obtained are given in Table 2B.

                                      Table 2A                                     __________________________________________________________________________     aLi.sub.2 O: bNa.sub.2 O: cMgO: 2.25F: 8SiO.sub.2                                                                   Dispersion                                                                     Time,                                     Sample                                                                              a    b    c    a + b                                                                               a + b + c                                                                             CEC  Minutes                                   __________________________________________________________________________      1   0.235                                                                               0.165                                                                               5.60 0.40 6.0    75   >120                                       2   0.200                                                                               0.200                                                                               5.60 0.40 6.0    75   >120                                       3   0.000                                                                               0.400                                                                               6.00 0.40 6.4    --   --                                         4   0.000                                                                               0.400                                                                               7.10 0.40 7.5    --   --                                         5   0.335                                                                               0.165                                                                               5.50 0.50 6.0    78   >120                                       6   0.250                                                                               0.250                                                                               5.50 0.50 6.0    80   >120                                       7   0.000                                                                               0.500                                                                               5.60 0.50 6.1    82   --                                         8   0.335                                                                               0.165                                                                               5.60 0.50 6.1    78   >120                                       9   0.200                                                                               0.300                                                                               5.60 0.50 6.1    78   >120                                      10   0.410                                                                               0.165                                                                               6.45 0.575                                                                               7.025  65   30                                        11   0.435                                                                               0.165                                                                               5.50 0.60 6.1    83   90                                        12   0.250                                                                               0.350                                                                               5.50 0.60 6.1    83   30                                        13   0.435                                                                               0.165                                                                               5.60 0.60 6.2    81   30                                        14   0.200                                                                               0.400                                                                               5.60 0.60 6.2    81   15                                        15   0.435                                                                               0.165                                                                               5.70 0.60 6.3    79   30                                        16   0.435                                                                               0.165                                                                               6.00 0.60 6.6    73   5                                         17   0.485                                                                               0.165                                                                               5.35 0.65 6.0    89   30                                        18   0.325                                                                               0.325                                                                               5.35 0.65 6.0    88   20                                        19   0.510                                                                               0.165                                                                               6.35 0.675                                                                               7.025  69   12                                        20   0.535                                                                               0.165                                                                               5.50 0.70 6.2    86   6                                         21   0.250                                                                               0.450                                                                               5.50 0.70 6.2    86   2                                         22   0.535                                                                               0.165                                                                               5.60 0.70 6.3    84   5                                         23   0.535                                                                               0.165                                                                               5.80 0.70 6.5    80   2.5                                       24   0.585                                                                               0.165                                                                               5.35 0.75 6.1    91   15                                        25   0.325                                                                               0.425                                                                               5.35 0.75 6.1    91   10                                        26   0.585                                                                               0.165                                                                               5.65 0.75 6.4    84   1.5                                       27   0.610                                                                               0.165                                                                               6.25 0.775                                                                               7.025  73   25                                        28   0.635                                                                               0.165                                                                               5.20 0.80 6.0    99   20                                        29   0.400                                                                               0.400                                                                               5.20 0.80 6.0    98   6                                         30   0.635                                                                               0.165                                                                               5.50 0.80 6.3    89   2                                         31   0.335                                                                               0.500                                                                               5.85 0.835                                                                               6.65   82   1                                         32   0.685                                                                               0.165                                                                               5.35 0.85 6.2    94   2                                         33   0.325                                                                               0.525                                                                               5.35 0.85 6.2    94   1                                         34   0.710                                                                               0.165                                                                               5.15 0.875                                                                               6.025  101  8                                         35   0.710                                                                               0.165                                                                               5.35 0.875                                                                               6.225  94   2.5                                       36   0.710                                                                               0.165                                                                               5.55 0.875                                                                               6.425  89   1.5                                       37   0.710                                                                               0.165                                                                               5.85 0.875                                                                               6.725  82   2                                         38   0.710                                                                               0.165                                                                               6.15 0.875                                                                               7.025  78   4.5                                       39   0.710                                                                               0.165                                                                               6.65 0.875                                                                               7.525  70   >60                                       40   0.735                                                                               0.165                                                                               5.20 0.90 6.1    99   2.5                                       41   0.400                                                                               0.500                                                                               5.20 0.90 6.1    99   2.5                                       42   0.735                                                                               0.165                                                                               5.35 0.90 6.25   95   1                                         43   0.735                                                                               0.165                                                                               5.45 0.90 6.35   92   1                                         44   0.735                                                                               0.165                                                                               5.55 0.90 6.45   90   1                                         45   0.735                                                                               0.165                                                                               5.85 0.90 6.75   84   1                                         46   0.785                                                                               0.165                                                                               5.35 0.95 6.3    96   1                                         47   0.835                                                                               0.165                                                                               4.90 1.0  5.9    110  5                                         48   0.835                                                                               0.165                                                                               5.00 1.0  6.0    102  10                                        49   0.500                                                                               0.500                                                                               5.00 1.0  6.0    108  6                                         50   0.835                                                                               0.165                                                                               5.20 1.0  6.2    101  1                                         51   0.400                                                                               0.600                                                                               5.20 1.0  6.2    101  1.5                                       52   0.885                                                                               0.165                                                                               4.75 1.05 5.8    117  60                                        53   0.935                                                                               0.165                                                                               5.00 1.1  6.1    109  2.5                                       54   0.500                                                                               0.600                                                                               5.00 1.1  6.1    109  >120                                      55   0.935                                                                               0.165                                                                               5.20 1.1  6.3    103  2                                         56   0.935                                                                               0.165                                                                               5.85 1.1  6.95   88   25                                        57   1.035                                                                               0.165                                                                               5.00 1.2  6.2    111  3                                         58   0.500                                                                               0.700                                                                               5.00 1.2  6.2    *    >120                                      59   1.085                                                                               0.165                                                                               4.75 1.25 6.0    109  >120                                      60   0.625                                                                               0.625                                                                               4.75 1.25 6.0    *    >120                                      61   1.135                                                                               0.165                                                                               5.00 1.3  6.3    113  4                                         62   1.135                                                                               0.165                                                                               5.40 1.3  6.7    102  12                                        63   1.135                                                                               0.165                                                                               5.80 1.3  7.1    93   25                                        64   1.135                                                                               0.165                                                                               6.20 1.3  7.5    86   >60                                       65   1.185                                                                               0.165                                                                               4.75 1.35 6.1    122  90                                        __________________________________________________________________________      *amorphous product                                                       

                                      Table 2B                                     __________________________________________________________________________     2% Dispersions in Deionized Water                                              Fann Viscosimeter Data                                                         Initial          After 24 Hours                                                                            After 48 Hours                                     Sample                                                                              a.V..sup.a                                                                          BYV.sup.b                                                                          %T.sup.c                                                                          A.V.                                                                               BYV %T A.V.                                                                               BYV %T                                         __________________________________________________________________________      1   1 j  0   20 1   0   27 1   0   29                                          2   1    0   22 1   0   30 1.5 0   28                                          3   1    0   12 9   10  24 13  41  26                                          4   0.5  0   12 1   0   14 1.5 0   15                                          5   1.5  0   24 2   0   30 6   5   34                                          6   1.5  5   25 4.5 0   26 9   28  29                                          7   1    5   17 2.5 0   24 4   0   26                                          8   1.5  0   30 3.5 0   29 6.5 5   82                                          9   1    0   20 1.5 0   28 6.5 5   28                                         10   8.5  41  18 20  143 26 27.5                                                                               194 28                                         11   2.5  0   24 14.5                                                                               59  44 17.5                                                                               61  46                                         12   1.5  0   23 7   5   39 13.5                                                                               33  42                                         13   2    0   31 14  36  57 18.5                                                                               74  60                                         14   2    0   28 8.5 8   47 16  46  49                                         15   3    0   31 17  56  54 20.5                                                                               79  58                                         16   4.5  0   41 18.5                                                                               77  67 21  102 71                                         17   3.5  0   35 14  36  58 16  51  62                                         18   3    0   33 16.5                                                                               51  51 19  87  52                                         19   12   64  21 24  171 31 31  212 33                                         20   4    0   66 20  77  87 22.5                                                                               97  91                                         21   2.5  0   39 14.5                                                                               36  66 23  89  71                                         22   5    0   71 20  66  91 22  92  92                                         23   5    0   54 18  71  83 21  99  85                                         24   2.5  5   48 11.5                                                                               18  75 16.5                                                                               41  77                                         25   2.5  0   29 9   5   42 14  26  46                                         26   8.5  18  70 22  102 88 23.5                                                                               128 89                                         27   16   79  21 28  191 31 33  222 32                                         28   2.5  5   47 7.5 10  73 12  31  76                                         29   2.5  5   45 16.5                                                                               56  65 21  97  70                                         30   6    0   78 20.5                                                                               79  92 23.5                                                                               92  93                                         31   13.5 59  26 19.5                                                                               122 43 23  128 46                                         32   2.5  0   86 17  51  93 21.5                                                                               82  93                                         33   4    0   46 22.5                                                                               89  78 26.5                                                                               122 82                                         34   3    0   78 7.5 0   92 12  13  92                                         35   5    0   87 19.5                                                                               66  92 23  87  92                                         36   6.5  5   83 19  71  88 20  87  88                                         37   11   37  67 19.5                                                                               92  82 20  97  85                                         38   13.5 77  37 20  120 55 21.5                                                                               128 62                                         39   9.5  26  19 19  102 33 24  117 35                                         40   2.5  5   88 14.5                                                                               41  93 20  66  95                                         41   2.5  0   49 22  94  76 25.5                                                                               122 82                                         42   4    0   90 22  77  93 24.5                                                                               82  93                                         43   4.5  0   87 21.5                                                                               61  90 23.5                                                                               92  90                                         44   8.5  0   85 21.5                                                                               92  89 23  105 88                                         45   13   46  76 20  97  84 21.5                                                                               112 84                                         46   3.5  0   89 23.5                                                                               92  91 26  107 92                                         47   1.5  0   71 11.5                                                                               14  85 23  86  88                                         48   2.5  5   64 4   3   80 8   5   86                                         49   2.5  0   35 18  54  55 22  87  61                                         50   3    0   85 21.5                                                                               82  88 24.5                                                                               102 89                                         51   3    0   17 16.5                                                                               51  32 20  87  36                                         52   2    0   25 3.5 0   38 8   0   37                                         53   2.5  0   85 22.5                                                                               87  88 25.5                                                                               112 88                                         54   1.5  0   9  2.5 0   12 4.5 5   13                                         55   3    0   85 23  82  88 26.5                                                                               122 88                                         56   17   117 26 27.5                                                                               214 37 29  263 38                                         57   6.5  3   77 24  105 86 26  107 85                                         58   2.5  0   25 13.5                                                                               38  39 15.5                                                                               56  42                                         59   14   36  67 28  145 80 32.5                                                                               194 81                                         60   17   102 39 33.5                                                                               245 53 34  265 56                                         61   6    38  13 10.5                                                                               56  23 11.5                                                                               61  23                                         62   4    13  16 5   13  19 5   15  20                                         63   2    0   22 16  59  40 22.5                                                                               84  45                                         __________________________________________________________________________      .sup.a A.V. = Apparent Viscosity, cp., at 1020 sec.sup.-1                      .sup.b BYV = Bingham Yield value, dynes/cm.sup.2                               .sup.c %T = Percent Transmission                                         

The data indicate that gellants which will disperse within 15 minutes at low shear at a concentration of 2% in deionized water to produce a sol having a low viscosity and a Bingham Yield Value less than 20 dynes/cm², which sol is converted on aging to a thixotropic gel having a Bingham Yield Value greater than about 50 dynes/cm², are obtained when 0.25≦a<1.1, 0<b<0.60, 4.75<c<5.85, 0.60<a+b<1.25, 6.0<a+b+c<6.65, and 0.7<CEC<1.2 Gellants which in addition to these rheological properties produce dispersions at 2% in deionized water having a clarity of at least 85% transmittance, are obtained when 0.50<a<1.05, 0≦b0.50, 5.0≦c<5.85, 0.60<a+b<1.25, 6.0<a+b+c<6.65, and 0.8<CEC<1.13 Gellants which produce dispersions having a clarity of at least 90% transmittance are obtained when 0.50<a<0.80, 0≦ b<0.50, 5.1≦c<5.7, 0.60<a+b<1.0, 6.025<a+b+c<6.4, and 0.8<CEC<1.0 Gellants which will disperse in deionized water at a concentration of 2% to produce dispersions having Bingham Yield Values in excess of 20 dynes/cm² are obtained when 0.25<a<1.1, 0<b<0.60, 5.85<c<7.0, 0.5<a+b<1.3, 6.5<a+b+c<8.0, and 0.70<CEC<1.0. The Bingham Yield Values of these dispersions increase with time such that thixotropic gels having a Bingham Yield Value greater than 50 dynes/cm² are obtained within 48 hours. Preferably 0.25<a<1.1, 0.1<b<0.5, 5.85≦c<6.5, 1.5≦d<3.5, 0.6<a+b<1.3, and 6.5<a+b+c<7.5.

Generally, as the sum (a+b+c) increases, the Bingham Yield Values of the dispersions after 48 hours increase and the % transmittance values of the dispersions decrease. When either c≦5.85, or (a+b+c)>6.65, the initial Bingham Yield Values are greater than 20 dnes/cm². When b>0.60 a smectite-type clay could not be synthesized and a totally amorphous product was obtained. Gellants having poor dispersion characteristics were obtained when either c≦4.75, (a+b)<0.6, or (a+b+c)>ca. 7.25. Generally poor gellants were obtained when either a<0.25 or (a+b+c) = 6.0.

EXAMPLE 2

Samples having the composition:

    0.67 Li.sub.2 O : 0.165 Na.sub.2 O : 2.25F : 8SiO.sub.2

were prepared at 18% solids in the following manner: MgO and HF were added to deionized water in the order indicated in Table 3 and mixed with a Lightnin Mixer for various periods of time as indicated in the table. Thereafter LiOH.H₂ O was added and mixed for the time indicated in Table 3. The silica sol was then added and mixed for 10 minutes before heating and mixing the suspension until a viscous slurry was obtained. The viscous slurry was placed in a sealed container at 100° C. The slurry gelled and the gel was aged at 100° C for 72 hours. A waxy solid was obtained which was dried overnight at 110° C. An additional sample was prepared by shearing the suspension for 2 minutes in a Waring Blendor before commencing the heating. Another gellant was produced by preparing the entire suspension in a Waring Blendor at low shear with a final 5 minutes of high shear before commencing the heating. The samples were evaluated as 2.5% dispersions in tap water. The data obtained are given in Table 3.

                                      Table 3                                      __________________________________________________________________________     MgO                  HF          LiOH . H.sub.2 O                                   Order of                                                                            Mixing     Order of                                                                            Mixing Mixing                                        Sample                                                                              Addition                                                                            Time, Min.                                                                            %   Addition                                                                            Time, Min.                                                                            Time, Min.                                    __________________________________________________________________________      1   1    5      9.5 2    5      5                                              2   1    15     9.5 2    5      5                                              3   1    30     9.5 2    5      5                                              4   1    60     9.5 2    5      5                                              5   1    1200   9.5 2    5      5                                              6   2    5      9.5 1    *      5                                              7   2    10     9.5 1    *      5                                              8   2    20     9.5 1    *      5                                              9   2    30     9.5 1    *      5                                             10   2    60     9.5 1    *      5                                             11   2    5      13.7                                                                               1    *      5                                             12   2    5      15.3                                                                               1    *      5                                             13   2    5      18.7                                                                               1    *      5                                             14   2    5      23.4                                                                               1    *      5                                             15   1    5      9.5 2    5      10                                            16   1    5      9.5 2    5      20                                            17   1    5      9.5 2    5      30                                            18** 2    5      9.5 1    *      5                                             19***                                                                               2    5      9.5 1    *      5                                             __________________________________________________________________________             2.5% in Tap Water                                                              Clarity              Bingham                                                   %           Apparent Yield                                             Sample  Transmittance                                                                              Viscosity                                                                               Value                                             __________________________________________________________________________      1      64          13.5     100                                                2      80          13.5      87                                                3      72          12.5      77                                                4      80          14        92                                                5      44           4        20                                                6      53           3        26                                                7      59          12       102                                                8      54          15       112                                                9      55          23       235                                               10      27           9        66                                               11      64           6        51                                               12      53          11        82                                               13      72          15       102                                               14      77          20       207                                               15      56           7        51                                               16      85          20       199                                               17      86          20       179                                               18**    86          13.5      97                                               19***   93          16       161                                               __________________________________________________________________________      *MgO added immediately after adding the HF                                     **Suspension after silica sol addition was given 2 minutes high shear in       Waring Blendor                                                                 ***Entire feed made in a Waring Blendor at low shear. The suspension afte      silica sol addition was given 5 minutes of high shear.                   

EXAMPLE 3

Samples having the composition

    0.735 Li.sub.2 O : 0.165 Na.sub.2 O : 5.3 MgO : df ; 8 SiO.sub.2

were prepared by the process of Example 1. The value of d was varied from 1 to 3.5. The samples all contained well crystallized trioctahedral smectite-type clays, as determined by x-ray diffraction. They were evaluated as in Example 1 for their ease of dispersion in deionized water, and for their turbidity. The data obtained are given in Table 4. The data indicate that gellants can be prepared when the number of fluorine atoms per unit cell of smectite-type clay is within the range from 1<to<3.5, preferably from 1.5≦to<3.5, more preferably 1.5<d<3.0.

                  Table 4                                                          ______________________________________                                         0.735 Li.sub.2 O : 0.165 Na.sub.2 O : 5.3 MgO : dF : 8 SiO.sub.2               2% Dispersions in Deionized Water                                              ______________________________________                                         Dispersion Fann Viscosimeter and Hach Meter Data*                              Time       Initial      48 Hours                                               d    Minutes   A.V.   BYV  %T   A.V.  BYV   %T                                 ______________________________________                                         1    6         6.5    10   29   36    173   65                                 1.5  2.5       8.5    15   73   33.5  217   85                                 2    1.25      7       8   84   28    173   90                                 2.5  4         2       0   84   23     87   94                                 3    0.75      8      13   80   18.5   82   86                                 3.5  2         2       0   83   20     79   91                                 ______________________________________                                          *A.V. = Apparent Viscosity, cp., at 1020 Sec.sup.-1 ± 0.5                   BYV = Bingham Yield Value, dynes/cm..sup.2                                     %T = Percent Transmission of light, Hach Meter                            

We claim:
 1. A process for synthesizing a composition containing a fluorine-containing trioctahedral smectite-type clay, said composition containing mole ratios of Li, Na, Mg and Si expressed as oxides, and F, of

    aLi.sub.2 O : bNa.sub.2 O : cMgO : dF : 8SiO.sub.2

where 0≦a< 1.2, 0≦b<0.60, 4.75≦c<7, 0<d<4, 0≦a+b<1.4, 5.5<a+b+c<8, and where c≦6 when a+b=0, said process comprising: a. forming an aqueous suspension containing from 12% to 35% solids by weight, the solids having the chemical composition represented by the formula above, by: (i) combining and mixing magnesium oxide, water, hydrofluoric acid, and a base selected from the group consisting of lithium hydroxide, sodium hydroxide, and mixtures thereof, until the base is dissolved; and (ii) adding a silica sol; b. agitating and heating the suspension until a viscous slurry is obtained from which no solids settle out; c. allowing the slurry to gel; d, hydrothermally reacting the gell under autogenous pressure at a temperature within the range from 85° C to about 250° C for a period of time sufficient to form said trioctahedral smectite-type clay; and e. drying the composition.
 2. The process of claim 1 wherein the apparant-viscosity of the viscous slurry is at least 10 centipoises.
 3. The process of claim 1 wherein said hydrothermal treatment is conducted at a temperature within the range from 85° C to 165° C for 4 to 120 hours.
 4. The process of claim 1 wherein said composition is dried at a temperature less than about 250° C.
 5. The process of claim 4 wherein the apparent viscosity of the viscous slurry is at least 15 centipoises, and wherein said hydrothermal treatment is conducted at a temperature within the range from 85° C to 165° C for 4 to 120 hours.
 6. The process of claim 1 wherein 0.25≦a<1.1, 0<b<0.6, 5.85≦c<7.0, 0.5<d≦3.5, 0.5<a+b<1.3, and 6.5<a+b+c< 8.0.
 7. The process of claim 6 wherein said magnesium oxide, said hydrofluoric acid, and at least a portion of said water are mixed together before adding said base.
 8. The process of claim 7 wherein the apparent vicosity of the vicous slurry is at least 10 centipoises.
 9. The process of claim 7 wherein said hydrothermal treatment is conducted at a temperature within the range from 85° C to 165° C for 4 to 120 hours.
 10. The process of claim 7 wherein said composition is dried at a temperature less than about 250° C.
 11. The process of claim 10 wherein the apparent viscosity of rthe viscous slurry is at least 15 centipoises, and wherein said hydrothermal treatment is conducted at a temperature within the range from 85° C to 165° C for 4 to 120 hours.
 12. The process of claim 1 wherein 0.25<a<1.1, 0.1≦b<0.50, 5.85≦c<6.5, 1.5<d<3.5, 0.6<+b<1.3, and 6.5<a+b+c<7.5.
 13. The process of claim 12 wherein said magnesum oxide, said hydrofluoroic acid, and at least a portion of said water are mixed together before adding said base.
 14. The process of claim 13 wherein the apparent viscosity of the viscous slurry is at least 10 centipoises.
 15. The process of claim 13 wherein said solid is dried at a temperature leas than about 250° C.
 16. The process of claim 13 wherein said hydrothermal treatment is conducted at a temperature within the range from 85° C for 4 to 120 hours.
 17. The process of claim 16 wherein the apparent viscosity of the viscous slurry is at least 15 centipoises and wherein said solid is dried at a temperature less than about 250° C.
 18. The product produced by the process of claim
 6. 19. The product produced by the process of claim
 9. 20. The product produced by the process of claim
 10. 21. The product produced by the process of claim
 12. 22. The product produced by the process of claim
 15. 23. The product produced by the process of claim
 16. 24. The product produced by the process of claim
 17. 25. A process for synthesizing a composition containing a fluorine-containing trioctahedral smectite-type clay, said composition containing mole ratios of Li, Na, Mg and Si, expressed as oxides, and F, of

    aLi.sub.2 O : bNa.sub.2 O : cMgO : dF : 8SiO.sub.2

where 0.25≦a<1.1, 0≦b<0.60, 5.0≦c<6.75, 0.5<d<4, 0.60≦a+b<1.4 and 6.0<a+b+c<8, said process comprising: a. forming an aqueous suspension containing from 12% to 35% solids by weight, the solids having the chemical composition represented by the formula above, by: (i) combining and mixing magnesium oxide, water, hydrofluoric acid, and a base selected from the group consisting of lithium hydroxide, sodium hydroxide, and mixtures thereof, until the base is dissolved; and (ii) adding a silica sol; b. agiating and heating the suspension until a viscous slurry is obtained from which no solids settle out; c. allowing the slurry to gel; d. hydrothermally reacting the gel under autogenous pressure at a temperature within the range from 85° C to about 250° C for 4 to 120 hours to form said trioctahedral smectite-type clay; and e. drying the composition.
 26. The process of claim 25 wherein the apparent viscosity of the viscous slurry is at least 10 centipoises.
 27. The process of claim 25 wherein said dryed composition is dried at a temperature less than about 250° C.
 28. The product produced by the process of claim
 25. 